1. Field of the Invention
The present invention generally relates to a progressive download method and system, and in particular, to a compatible progressive download method and system using meta data.
2. Description of the Related Art
In general, a content download service refers to a service which enables a Web client to download specific multimedia content from a server, store the downloaded multimedia content in its local memory, and repeatedly play the stored multimedia content. Since a conventional download methods use a Hyper Text Transfer Protocol (HTTP) and perform reliable data transmission/reception through a Transmission Control Protocol (TCP) transmission, data loss is minimized and high display quality can be provided once downloading has been completed. However, according to conventional download methods, content that is being downloaded cannot be played until the downloading has been completed.
A data transmission process according to conventional download methods using the TCP will be described with reference to FIG. 2A. In FIG. 2A, when a terminal 200 and a server 210 are TCP connected through a network, the terminal 200 transmits an x.mp4 request for an mp4 format file having a specific range to the server 210. Upon receipt of a response signal 200 OK to the x.mp4 request, the terminal 200 downloads a corresponding x.mp4 file and releases TCP connection. In this way, data transmission/reception is performed.
A data transmission process according to a conventional resumable download method will be described with reference to FIG. 2B. In FIG. 2B, downloading of a file is interrupted by an internal or external factor. In this case, after a timeout as indicated by 220, a request for resuming the downloading of the file is transmitted to the server 210. Since the terminal 200 knows the range of the file that has been downloaded so far (i.e., before the time out), the terminal 200 informs the server 210 of the range of the file that has been downloaded to download the remaining range of the file.
A streaming method regarded as a representative real-time application in terms of data transmission through a network uses a User Datagram Protocol (UDP) transmission having no retransmission capability at a specific transmission rate. The streaming method performs real-time transmission/reception through UDP transmission that requires a more complex and unreliable control process than content downloading, and has a high possibility of experiencing errors and/or data loss. Since streaming data having a data loss is stored in a local memory, quality that is equivalent to that of the original content cannot be provided when the stored data is played, if there is a data loss.
As an alternative to the foregoing two methods, there is a progressive download method suggested by the 3rd Generation Partnership Project (3GPP). The progressive download method is targeted for a *.3gp format file basically based on MPEG4 (Motion Picture Experts Group-4) and is defined in the 3GPP TS26.244 standard. The progressive download method can play content that is being downloaded, thereby ensuring high display quality without a data loss and providing a real-time service. With these advantages, some European General Packet Radio Service (GPRS) and Universal Traffic Management Systems (UTMS) network operators are actively introducing the progressive download method.
However, the progressive download method has the following constraints.
First, the streaming method uses the UDP transmission having no retransmission at a specific transmission rate, whereas the progressive download method uses the reliable transmission protocol TCP download and storage of storing time-insensitive files as opposed to real-time playback of files. For example, in the progressive download method, downloading may be temporarily interrupted due to flow control and retransmission provided by TCP transmission, resulting in degradation of a real-time feature in a real-time application.
The progressive download method has a constraint in the creation of content in view of data storing. The 3GPP TS 26.244 V6.0.0 standard prescribes a 3gp file format for a progressive download service. In the 3GPP TS 26.244 V6.0.0 standard, a profile of a file is prescribed as ‘3gr6’, a ‘moov’ box in the 3gp file must be positioned immediately after an ‘ftyp’ box, and the two boxes (or atoms) must be positioned at the head of the 3gp file. In addition, all media tracks must be interleaved by an interval of 1 second or less.
However, a general MPEG4 content file has various formats as shown in FIGS. 1A through 1C. FIGS. 1A through 1C illustrate various formats of a general MPEG4 content file.
In a 3gp format content file named sharp.3gp in FIG. 1A, a file name sharp.3gp 100 is followed by an ‘ftpy’ box indicating a file type and the ‘ftpy’ box is followed by an ‘mdat’ box 105 that is followed by a ‘moov’ box 110. This file has a 3gp file format, but internally, its video data composed of 22 frames has an H.263 format and its audio data composed of 21 frames has an AMR (Adaptive Multi-Rate) format.
In contrast, in FIG. 1B, a file name aking.mp4 115 is followed sequentially by an ‘ftpy’ box, an ‘udta’ box 120, a plurality of ‘mdat’ boxes 125, and a ‘moov’ box 130. In the file shown in FIG. 1B, video data has an MPEG4 format and audio data has the AMR format.
In FIG. 1C, a file name vfuk.3gp 135 is followed sequentially by an ‘ftpy’ box, a ‘moov’ box 140, and an ‘mdat’ box 145. In the file shown in FIG. 1C, both video data and audio data have the MPEG4 format. As shown in FIGS. 1A through 1C, since the MPEG4 content file does not comply with the prescription suggested by the 3GPP, the progressive download method cannot be applied to conventional content files created without complying with the 3GPP prescription.
However, the 3GPP does not suggest an alternative progressive download method that is compatible with conventional content in a wireless network. Nevertheless, there is an increasing demand for an alternative technique that is compatible with conventional content as the progressive download method prescribed only for a 3G network is evolving towards a 4G technique aiming at integrating wired and wireless networks and establishing an open architecture. For example, some of representative European GPRS (General Packet Radio Service) and UTMS (Universal . . . ) network operators such as Vodafone allow terminal users to access a Web server on an external Internet of the UTMS network through a Uniform Resource Locator (URL) input and to download desired content. However, contents of almost all servers on the Internet are created with no regard to the 3GPP standard and it is practically impossible to recreate the created content according to the 3GPP standard.
As described above, although being capable of playing content that is being downloaded, a conventional progressive download method cannot be used when content created without regard to the 3GPP standard is downloaded.